Drum forming machine



Aug- 28, 1962 o. J. VAN LEER ETAL 3,051,112

DRUM FORMING MACHINE 3 Sheets-Sheet 1 Filed Aug. 8, 1958 Aug. 28, 1962 y O. J. VAN LEER ETAL DRUM FORMING MACHINE 3 Sheets-Sheet 2 Filed Aug. 8, 1958 l INvEN-rons OscAaJvAN LEER CHmsTlAN RAaETm $3. @Miam JWM ATTYS,

Aug. 28, 1962 o. J. VAN LEER ETAL DRUM FORMING MACHINE 3 Sheets-Sheet 3 Filed Aug. 8, 1958 INVENToQs OSCAR J. VAN LEER CHRISTIAN RAGETTLI 6.3'. Mia-v W JM A'rvvs.

3,05Lll2 Patented Aug. 28, 1352 v.ice

3,051,112 DRUM FRMING MACHINE @scar J. van Leer, Barrington, and Christian Ragettli, Chicago, Ill., assignors to Grotnes Machine Works, Inc., Chicago, Ill., a corporation of Illinois Filed Aug. 8, 1958, Ser. No. 753,934 6 Claims. (Cl. 113-44) The present invention relates to drum forming and more particularly to a device for forming a corrugated and hanged sidewall of a shipping drum or the like.

In the past, forming the sidewall of a shipping drum has required use of a line of machines with the cylindrical blank being passed from one machine to' the next for a succession of operations. These operations have included expanding of the blank, expanding of the beads, expanding of the intervening corrugations and the formation of the end anges. As a result, a drum forming production line has been a matter of considerable expense. Moreover, it is usually impractical to install an elaborate layout such as that outlined above in remote outposts throughout the world where the drums are filled for shipment.

Accordingly, it is an object of the present invention to provide a drum forming device which is capable of forming the beads, corrugations yand ilauges in a single operation. It is a related object to provide a drum forming machine which is extremely rapid in operation, forming a finished product with the blank ina single position within a matter of seconds.

It is another object to provide a drum forming device which is simple in construction, inherently strong, 'and which is well adapted for -use under rugged field conditions. It is a related object to provide a drum forming device which requires little maintenance and which may be operated for long periods of time by untrained and uneducated personnel.

In one of the aspects of the invention it is an object to provide a drum forming device which is hydraulically operated but which employs only a small volume of fluid -to expand the blank from its initial condition to its fully corrugated and anged condition. It is a further object to provide a device of the above type in which sufficiently high pressures may be safely developed to form beads and corrugations and in `which the beads and corrugations may be deep and well defined.

It is still another object or" the invention to provide a drum forming device in which the integrity of the metal is maintained, i.e., in which the drum may be formed without any thin or weak spots and in which successful operation is possible using a wide variety of metals. It is therefore an object to provide a drum forming procedure and machine which permits the drawing of relatively deep beads without developing localized stress in the blank. In this connection, it is an object to provide a device of the above type which produces an unmarred end product free of the usual scratches and die marks as associated with conventional forming procedures, making it possible to form drums which are prepainted or preiinished without scratching or chipping the finish or causing it to peel.

In one of its aspects, it is the object of the invention to provide a drum forming machine employing a rubber blanket in contact with the inner surface of the blank so that such inner surface may be kept dry and free of oil. Use of such blanket, moreover, results in an even distribution of stress, as previously mentioned. It is, moreover, an object to provide a novel blanket arrangement including means for anchoring the blanket and for contributing to the long life of the blanket. In one embodiment of the present invention a novel blanket arrangement is employed comprising two or more layers of rubber with a volume of hydraulic fluid in between, which results in a number of advantages; for example, :a reduction of localized shear stress in the making of bends,

which is a frequent cause of failure and the breakdown of the rubber structure in prior devices employing rubber blankets.

All other objects and advantagesof the invention become apparent in the attached detailed description in which:

vFIGURE 1 is a vertical section View of a drum forming device employing the present invention.

FIG. 2 is a section taken along the line 2-2 in FIG- URE 1.

FIG. 3 is a fragmentary section taken along7V the line 3 3 in FIG. 1 and showing the construction and operation of the retaining ring.

FIG. 4 is a fragmentary section somewhat enlarged showing the flanging portion of the device together with Vthe stop mechanism.

FIG. 4a is a fragmentary section showing the action of the blank-inserter member.

FIG. 5 is ra diagrammatic fragmentary view of the stop member showing the self-centering action which occurs upon insertion of a blank into working position.

FIG. 6 is a fragmentary section based upon FIG. l and showing the beginning of the formation of the flange.

FIG. 7 is a fragmentary section similar to FIG. 3 but showing the flange fully formed.

FIG. 8 is a fragmentary section showing the beginning of the formation of the beads and corrugations.

FIG. 9 is a fragmentary section similar to FIG. 8 but4 showing the beads and corrugations fully formed and seated prior to releasing the hydraulic pressure and retracting the `outer dies.

FIG. l0 is a fragmentary view of the lower right-hand portion of FIG. 1 but showing a modied form of blanket comprising two layers.

While the invention has been described in connection with a preferred form of machine, it will be understood that we do not intend to limit ourselves to the particular embodiment of the invention but rather intend to cover all modilications and alternative constructions falling within the spirit and scope of the appended claims.

Turning now to FIGS. l and 2, the drum forming device Itl includes a supporting frame 11 and an outer die assembly which in the present instanceis made up of a series of complementary segments 12. These segments are ten in num-ber in the illustrated machine. For squeezing the segments 12 inwardly, toggle links 13 are provided. These links are pinned at their outer ends to an outside or operating ring 14. Power operated means (not shown) are provided for oscillating the ring through a small arc for clamping and retracting the die segments. In order to guide the segments 12 for radial movement, retaining rings 15 are employed having inwardly extending guide surfaces 16 lbearing against radial abutments 17 formed on bearing sections 12a. 'Ihe retaining rings 15 are supported within the structure on axially extending posts 18 spaced at intervals about the periphery. Thus, it will be apparent that when the operating ring is rotated in a clockwise direction, bearing sections 12a, 12 will be `drawn radially outward and thus release the die segments 12. As will become apparent, this releases the completed work so that it may be removed from the machine. When the operating ring is rotated in the opposite or counterclockwise direction the segments will tend to remain stationary. This assumes that the length of the links 13 is such as to produce a shallow toggle angle, i.e., approaching the dead center condition so that the radial component of force is substantially greater than the peripheral component. The friction between the heavy die segments and the base may be relied upon to resist the peripheral component but if there is nevertheless any tendency toward peripheral movement, the amount of such movement is limited by interference 'between the abutments andv the inward extensions of the stationary Vring 15.V Y

More detailed attention will next be given to the con- Y struction of a typical one of the `die segments. As shown in FIG. l, the segment 12 mounts die inserts 21, 22 for forming beads in the drum as Well as inserts 23, 24, 25 forming the intervening corrugations which are usually of a lesser depth. The die inserts may be fastened in place by any desired means, preferably recessed screws.

Inaccordance Vwith the presentY invention, a resilient cylindrical blanket formed or rubber or the like is pro-V `and the dies prior to application of the .forming pressure.

ForY the purpose of mounting the blanket at its ends and to seal same against the escape of fluid pressure, a set of conic-al clamps is provided at the upper and lower ends. As shown in FIG. 1, the lower clamp `comprises an outer member 40 having a conical clamping surface 41 and an inner 'clamping member 42 having a clamping surface 43. The clamping surfaces 41, 43 may be straight as shown or may be provided with mating convolutions for iirmly gripping the end of the blanket. In order to draw the two clamping members together, a ring of bolts 45 is employed, spaced at equal intervals about the periphery.

At the upper end, the outer clamping member 50 has a clampingrsurface `51 and mates with an inner clamping member 52 having a surface 53 and with the clamping pressure being provided by bolts 55. V ,In accordance with one of the aspects of the invention, the space inside of the rubber blanket 35 is al-V most completely occupied by a non-yielding cylindrical ller member, thereby greatly reducing the amount of hydraulic fluid required in order to pressurize and fully expand the 'blanket into contact with the blank. In the present instance, the core member is in the form of a cylindrical plate 60 which is welded or otherwise suitably secured at its upper and lower edges to inner members 42, 52 as shown. In order to admit hydraulic fluid to the space *between the ller member and the blanket, a suitable opening 61 is provided which is connected to hydraulic supply line In accordance with one of the important aspects of the present invention, an abrupt annular shoulder is pro vided vat at least one end of the die assembly having au annular clearance space adjacent thereto, and the resilient blanket is axially extended beyond said shoulder so that with a cylindrical blank freely overhanging said shoulder, expansion of the resilient blanket underhydraulic pressure causes the overhanging portion of the blank to be deformed in said clearancespace into a radially extending flange. In the present Vinstance the abrupt shoulder indicated at 65 in the drawings is bounded by a clearance lspace 66, the overhanging portion of the blank bein-g indicated at 30a.

l Moreover, it is a further Vfeature of the invention that the clearance space Vis bounded by a smoothly curved and smoothly continuous wall for seatingly supporting the blanket when the blank 1s expanded by hydraulic pressure. In the present instance the Wall indicated at 67 is formed on an annular supporting member 63 which is not segmented but which extends 1n a continuous circle free? of any interruptions or sharp edges. In cross section the space 66 is formedv in what may be termed a semi-heart shape having its deepest portion adjacent the flange and tapering inwardly to the point of anchoring of the blanket. Preferably the axial thickness of the upper portion of the supporting member 68, and which is indicated at 69, is such as to exceed the thickness of the blank by a relatively small amount. Moreover, the upper portion of the supporting member extends inwardly only a limited amount, thereby providing clearance for formation and seating of the flange. Y

The importance of the `above arrangement will be'apparent upon considering what occurs during a typical operating cycle. First, the blank is inserted so that it occupies the position shown in FIGS. l and 4. Upon applying hydraulic pressure inside of the blanket, the blanket tends to expand or balloon out into the clearance space 66 `acting against the overhanging portion 30a of the blank. It is found that when using steel blanks of conventional thickness only limited pressure on the order of a few hundred pounds per square inch is required to begin formation of the'ange about the shoulder 65, as illustrated in FIG. 6. Continued application of pressure causes the flange 30a to be swung through the clearance space 66 and fully seated l'against the shoulder 65 as shown in FIG; 7. The pressures required for this are sufficiently low so that the lower edge of the blank does tions further show that substantially higher pressures are required for the formation of the beads and corrugations than are required for the full formation ofV the ilange. Thus Vthe smooth annular surface 67 referred to above serves the important purpose of supporting the balloonedout'portions of the blanket against damage in the face of the pressures, on the order of 200G-600() lbs. per square inch, required for the `deformation of the blank into the corrugated `and beaded portions of the dies. The successive deformation of the walls of the drum is illustrated in FIGS. 8 and 9, FIG. 8 showing the beginning of the deformation at about SOO-1000 klbs.-per square inch, `and FIG. 9 showing full deformation at a much higher pressure, say on the order of 400G-6000 lbs. Thus as a result of'progressive increase of pressure within the blanket, a sequential operation is produced, as illustrated in the series of FIGS. 6-9, with the flange being fully formed followed by the corrugation of the side walls. However, it should be noted that the entire pressure cycle lfrom atmospheric to 6000 lbs. may be completed on a production line basis in a very short space of time, for example, on the order of one second. This rapid build-up of high pressure is rfacilitated by the fact that tremendous pressures may be produced 'by entry of only a small amount of fluid ydue to the limited annular space which exists between the ller member 64B and the inner wall of the blanket. Thus a low capacity pump will suflice to attain the required high pressures and the friction of the fluid in the Huid lines is not a problem.

In accordance with one of the detailed aspects of the invention, a novel stop means is pro-vided for positioning an inserted blank so that it overhangs the ange-forming shoulder 65 by the desired amount. More specifically, 'an annular stop member is provided in the form of a ring having an internal conical surface, with the stop member being axially movable betweenan upraised position in which it engages'th'e'leading edge of the blank for positioning purposes and a lowered position in which the conical .sur-face' merges smoothly with the curved annular supporting surface 67 previously mentioned. In the present device the annular stop member indicated at 80 has an internal conical supporting sur-face S1 'at its upper edge. The thickness of the supporting member 80 is such that the advancing edge of the blank is engaged on the tapered surface regardless ofthe position of the blank Within the narrow annular work space. The result is to produce positive stoppage of the blank through a centering action regardless of the position of the blank laterally and regardless of whether it is in precise cylindrical form at the time it is inserted. This is brought out in FIG. 5 where it will be noted that the conical surface 81, in the usual case, will engage only a portion of the leading edge of the blank indicated at 82. Forcible insertion of the blank causes the edgerportion 82 thereof to ride downwardly on the conical surface so that the blank occupies the positively seated and centered position shown by the dotted outline in FIG. 5. Thus even though the stop surface is tapered or conical, positive stoppage at a precise point with the same overhang at each end is assured. Insertion forces on the order of 100 lbs. may be employed in the practical case of a 50- gallon drum.

In order to absorb the reactive force, the annular stop member 80 may, upon retraction, be nested in an annular receptacle in the supporting member 68. To move the stop member between its two positions, push rods 85 are provided at spaced intervals about the ring and threaded into the ring as shown, the push rods being received in holes 86 bored axially in the member 68. Any desired means may be provided at the outer ends of the push rods for applying force thereto, for example, a positioning ring S7 movable between two axial positions.

For the purpose of supporting the ballooned-out portion of the blanket, which causes formation of the upper flange, in the face of the high pressures required for forming the beads and corrugations an -annular filler member 86a is provided which -smoothly bridges the mouth or gap into which the blanks are inserted into working position.- The filler member 80a is, in profile, the same shape as the stop member 80 previously referred to and forms a smooth continuation of the supporting surface 67a. To block the filler member 30a in position upon application of pressure inside of the blanket 35, a suitable locking member Sill?, which is indicated by the dot-dash outline, may be employed, such blocking member being removable for entry of the blank. It will be apparent to one skilled in the art that the present invention is not limited to any particular form of blocking means, and if desired a shotpin or the like may be employed for locking the filler member 80a in place after it is inserted into the position shown.

In accordance with one of the more detailed features of the invention, the filler member 80a performs the function of an inserter as shown in FIG. 4a. In this figure the member Stia is in process of pushing the blank 30 into place, it being understood that `the stop Si? (FIG. 4) isin upraised position to receive the oncoming blank. Inserting pressure is applied to the member `80a by any suitable means, and the member is advanced to an extreme position 91 as required to seat the blank in working p'osition. The blank is maintained in such working position by the initial expansion of the blanket 35, following which the members 80, 89a, are both retracted, the member 80a being retracted into the flush position indicated at 92 (FIG. 4a) in which the face 81a thereof -merges smoothly with the supporting surface 67a.

While the operation of the device will be apparent from the foregoing description, it will be helpful to briefly summarize the sequence which occurs during a typical cycle consuming no Imore than a few seconds. First of all, the die operating ring 14 is rotated counterclockwise (by means not shown) (FIG. 2) into the toggled clamping position in which all of 'the diesegm'ents are rmly supported, and together form a substantially continuous die surface. The upper filler member 80a is reti-acted to an out of the way position. The lower or stop member is raised by a suitable operator 87 to a predetermined upraised position shown dotted in FIG. 4 and depending upon the desired width of flange. The blark is then inserted and pressed downward by the annular member 80a so that it seats continuously upon the tapered surface 8.1. Following this, hydraulic uid is -applied through the orifice 61. As soon as suthcient pressure has been built up to hold the blank in place, which happens in a small fraction of a second, the `stop member Sit and the filler member 89a are both forcibly withdrawn into the seated positions shown in FIG. 1. The blocking means 80h is moved into blocking position. The build-up of pressure Iwhich occurs immediately thereafter results in the expansion cycle illustrated in FIGS. 6-9 with formation of the flange and bodily expansion of the blank into contact with the die segments, followed by formation of the beads and corrugations. After the latter are formed, the pressure is immediately released. Because of the small amount of contained fluid, such release occurs very quickly, on the order of -a second or less. Simultaneously with such release, the die positioning ring 14 is rotated clockwise, thus tensioning the operating links 13. The interference between the retaining surfaces 16 and the abutments 17 on the `die segments insures that the die segments are guided `radially outward, thereby freeing the beads 4and flanges [and the blocking member 8% is removed so that the completely formed blank may be axially withdrawn for insertion of the neXt blank in the series, following which the cycle is repeated.

It will be apparent to one skilled in the art that the present machine performs, in a working cycle of only a few seconds, all of the successive beading, corrugating and ilanging operations which have been performed in .the pastby a series of machines and which have required a blank to be successively positioned in a series of work stations. VNot only is the total forming operation reduced to only-a small fraction of the time previously required, but simultaneous performance of all of the operations with the blank in a single position insures that the beads, corrugations and flanges will all occupy exact positions relative to one another. The amount of handling and labor required in the production of a drum is greatly reduced.

In addition 4to the saving in the investment requined for production, it is to be particularly noted that the device consists of a minimum number of compact simply formed parts, thereby permitting the entire machine to be easily transported into inaccessible areas and to be operated and maintained by unskilled and uneducated personnel.

-The fact that the blanket operates simultaneously upon all areas of the blank insures that pressures are evenly ydistributed over the blank `and the localized stresses are avoided. Consequently, blank-s formed by the present procedure are stronger and more luniform than blanks formed -by the prior mechanical means. Moreover, since the blank is smoothly and gradually acted upon by the blanket over all of its area simultaneously, the blank may be pre-finished,V or pre-printed without danger that the nish will be marred or chipped during the forming operation. 'l'he usual die marks normally found on drums are avoided.

Subsequent Vto forming the drum sidewall by use of the present machine, a conventional seamer may be employed to secure the top and bottom of the drum in place.

While the -above `discussion has been directed to a blanket 35, certain additional advantages may be achieved by employing a blanket consisting of several thicknesses of resilient material with a limited amount of hydraulic fluid trapped between them as shown in FIG. l0. In the latter ligure, the composite blanket is indicated at 9S, and

each of the thicknesses may have la dimension about half of that shown in the previous embodiment. The amount of hydraulic fluid should be suicient so that the portions of the blanket are kept separated over the greater part of their surface area and the fluid should occupy a small but appreciable fraction of the total volume occupied by the blanket. Our observations show that a composite blanket with iiuid between the layers greatly facilitates bending 'aroundY sharp corners without developing undue shear stresses so that the le and capability of the blanket are substantially increased. It is found that the layers of the blanket come into contact, with the inner layer giving direct physical support to the outer layer, at the very points where shear stresses would normally tend to be developed, i.e., around corners, with the blankets remaining out of contact and separated by uid over the areas of lesser shear stress.Y While a vcomposite blanket comprising two Ilayers with fluid in between has been -illustrated, it will be apparent to one skilled in the art that the invention is not limited thereto and additional thicknesses or layers, separated by uid, may be employed. i

While the invention has been described as embodied in a cylindrical `shipping container, the invention is obviously not limited thereto but is applicable to containers or sleeves having a continuous wall but of 'various shapes and sizes. Thus in the following claims the tet-ms drum, drum shaped, and continuous are intendedV to cover all geometrical surfaces having an Iaxis and in which any cross section taken perpendicular tothe axis forms a closed loop. .l i

VWe claim as our invention:

l. Ina machine for forming a drum from a generally cylindrical workpiece or blank, the combination comprising a base, a stationary hollow cylindrical core Von said base, a generally cylindrical segmented die member on said base and having an abrupt shoulder at at least one of its ends, anannular support member for supporting said die member adjacent said Yshoulder, a resilient cylindrical blanket of rubber or the like surrounding said cylindricall core within said die member and extendingaxially beyond said shoulder, means for enclosing the ends of the blanket, said die and blanket together defining fan annular work space for insertion of the workpiece, said annular support member being relieved to provide a clearance space adiacent said shoulder, a stop member having an engaging surface movable into said clearance 'space` to contact said blank for positioning the end thereof so that it overhangsV saidshoulder into said clearance space, and means for applying hydraulic pressure within said blanket iso that Vexpansion thereof causes saidV blanket to bear against the overhanging portion of the blank to formrs'aid overhanging end portion about said Ishoulder into a` radially extending flange, the support member having a smoothly continuous wall for seating the portion of the blanket which is expanded into said clearance space incident to formationV of said flange, said stop member having provision for retracting lthe same from said space, vfollowing positioning of the workpiece, to a retracted position in which the Vstop member engaging surface is ush with said wall.

2. In a machine for forming a drum from a cylindrical workpiece or blank, the combination comprising a base, a stationary hollow cylindrical core on said base, an upper head ,secured to the top of said core, a lower head secured to the bottom of said core, a cylindrical blanket having its upper and lower ends sealingly secured in said heads respectively to deiine an annular pressure space having iiuid therein, a cylindrical die assemblyY including a set 'of outer dies surrounding said blank and said heads to define an annular space therebetween for insertion of the workpiece, an annular support member surrounding said lower head for supporting said Adie assembly, means for applying pressure to the uid between said core member and the blanket for inliating the same for pressing the workpiece outwardly against said dies and, a ller member slidable within said support member and interposed between y atleast one of said heads and said, die assembly Vand having a surface for contacting the -workpiece to position the latter and being retractable into said support member vfor supporting the portion of the inated blanket which extends beyond said workpiece.

3. In a machine for forming a drum from a cylindrical or blank, the combination comprising a base, a stationaryy workpiece or blank, the combination comprising a base, a stationary hollow cylindrical core on said base, an upper head secured to the top of said core, a lower head secured to the bottom of said core, a cylindrical blanket having its upper' and lower ends held by said yheads respectively, a cylindrical dieV assembly including aset of outer dies.V surrounding said blank and said heads to deiine an annular space therebetween for insertion of a cylindrical workpiece, annular support 'members surrounding said upper and lower heads for supporting said die assembly, means for 'applying pressure between said core member and the blanket for inilating the same for pressing the workpiece outwardly against said dies, and upper and lower iiller members slidable within said support members interposed between at least one of said heads and said die assembly, and each having a surface for contacting the workpiece to position the same and being retractable into said support member for supporting the portion of the inflated blanket which extends beyond said workpiece.

4. 'In a machine for forming a drum from a cylindrical workpiece or blank, the .combination comprising a base, a stationary hollow cylindrical core on said base, an upper head secured to the top of vsaid core, a lower head secured to the bottom-of said core, a cylindrical blanket having its upper and lower ends held by said heads respectively, a cylindrical die'assembly including a set of outer dies surrounding said blank and said heads to define an annular space therebetween for insertion of a cylindrical workpiece, annular support members surrounding said upper and lower heads forsupporting said die assembly, means for applying pressure between )said core member and the blanket for inating the same for pressing the workpiece outwardly against said dies, and upper and lower filler members slidable within said support members and interposed between the respective heads and saidv die assembly, said iiller members each-having a surface for contacting the workpiece to lposition the same and being retractable into said support member for supporting the portion of the inflated blanket which extends beyond-said workpiece, said lower iiller member being vertically movable between an upper limit position in which said ller member serves as an insertion stop for the workpiece and a lower position in -which the surface of. the iller member serves as a support for the portion of the blanket which extends ,axially beyond the workpiece.

e 5. In a machine `for forming a drum from a workpiece hollow cylindrical core on said base, a generally cylindrical segmented `die member on said baserand having an abrupt shoulder at one of its ends, an annular supporting member for supporting said diel member adjacent said shoulder, a resilient cylindrical blanket of rubber or the like surrounding said cylindrical core within said die member and extending axially beyond said shoulder, means for enclosing the ends of the blanket, said die member and blanket together defining an annularrwonk space for receiving the workpiece, said `annular supporting member being relieved to provide a clearance space adjacent said shoulder, a stop having a Vsurfacevfor positioning said workpiece so that the end thereof o-verhangs said shoulder adjacent said clearance space, means for retracting the' stop after the workpiece has been positioned, and means forrapplying hydraulic pressure within said blanket so that expansion thereof causes said blanket to bear against -the overhanging portion of the workpiece to form said overhanging portion about said shoulder into a radially extending ange, the supporting member having a smoothly continuous wall for seating the portion of the blanket which is expanded into said ciearance space incident to formation of said iiange.

6. In a-machine for formingY a drum from a blank workpiece, the combination comprising a base, a stationary hollow cylindrical core on said base, a generally cylindrical die on said base and having a corrugated inner surface and terminating in a relativelyl abrupt annular shoulder at one of its ends bounded by an annular clearance space bounded on its outward side by a surface facing said core, a cylindrical blanket formed of rubber or the like surrounding said cylindrical core and telescoped within said die and together with the die dening an annular work space for insertion of a cylindrical metal Iblank, means for enclosing the ends of the blanket, stop means for engaging7 `the advancing edge of an inserted rblank for positioning the same in overhanging relation with respect to said shoulder, said blanket being axially extended beyond said shoulder, means for applying hydraulic pressure Within said blanket for expanding the same outwardly against said workpiece so that the overhanging portion of the blank is formed about said shoulder into a radially extending ange and so that the wall of said blank is deformed to said die, said stop means being retractable to allow the blanks to be deformed following positioning of said stop means into a retracted position clear of the blank and in which the stop means yforms a smooth continuation of said surface facing said core, the latter surface supporting said blanket throughout its entire surface against further deformation incident lto the application of the higher pressures required for forming the corrugations in said side Wall.

References Cited in the Ile of this patent UNITED STATES PATENTS 701,549 Deering .Tune 3, 1902 1,941,406 Bauroth Oct. 15, 1912 1,930,745 Fisher Oct. 17, `1933 2,579,919 -Funke Dec. 25, 1951 2,742,873 Moore Apr. 24, 1956 2,761,405 Moller Sept. 4, 1956 2,821,945 Peccerill Feb. 4, 1958 2,849,977 Nielsen etal Sept. 2, '1958 FOREIGN PATENTS 509,339 Italy Jan. 13, 1955 

